Icosahedral virus

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A virus icosahedron (20-sided structure) shown in the (left) twofold, (centre) threefold, and (right) fivefold axes of symmetry. Edges of the upper and lower surfaces are drawn in solid and broken lines, respectively.

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Animation of an icosahedral (20-sided) virus.

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Animation and microphotography illustrating the structural diversity of viruses.

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structure

...the capsid is further enveloped by a fatty membrane, in which case the virion can be inactivated by exposure to fat solvents such as ether and chloroform. Many virions are spheroidal—actually icosahedral—the capsid having 20 triangular faces, with regularly arranged units called capsomeres, two to five or more along each side; and the nucleic acid is densely coiled within. Other...

...vary greatly in size, from 20 to 150 nm in diameter, essentially proportional to the size of the nucleic acid molecule coiled up inside the virion. Most, if not all, of the polygonal viruses are icosahedral; like a geodesic dome, they are formed by equilateral triangles, in this case 20. Each triangle is composed of protein subunits (capsomeres), often in the form of hexons (multiples of...